Hi Martin,
I had several years of doing this work in the RMAS (MoDn), after the 1996 contract a inspection on a light buoy meant retrieving everything, then breaking it down into its component parts and measuring it. The allowance was 11% wear of original size, worn parts where renewed and the whole lot remade and laid to a position tolerance of +/- 15ft.
The mooring was a steel clump of ethier 3 or 5 tons have known 7t, the risers where 38mm open link chain the riser being made to length reuired for depth, this leads to a 38mm box swivel which then is attached to the buoys bridle whichis made of 2 legs of 38mm OEL chain. The Trinity house have a similiar arrangement except they use 38mm chain cable.
The vessel positions herself alongside the buoy first to check position. The Sal class would drop a stern anchor lying to 3/500 ft of wire using the forward 380 degree thrust bow thruster to maintain position. Then the gemini is launched and its crew pass a chain snotter connected to a recovery wire, which is lead through the side rollers to the forward 7t capstan. On completion of this the crane is slewed out and the gemini crew connect the crane lifting strops into the buoy.
Then the capstan heaves in on the recovery wire, hopefully if the wire and chain are correctly plced the chain snotter clenchs under the bridle swivel, when the swivel breaks the surface, the buoy is lifted out of the water, when it is possible a working main wire is now connected into the riser chain below the swivel, when this is done and the main has the weight then the bouy is brought in board and disconnected. After this the after main heaves awy until the clump comes level with the side rollers and the clump is recovered using the crane.
The trinity house tenders do the work in a slightly different but more efficient manner as thier boats are designed for only buoy work where as the RMAS vessels are multi purpose.